1-Chloronaphthalene and 2-chloronaphthalene were metabolized by pseudomonads able to degrade naphthalene, but the chloronaphthalenes did not support growth. Their metabolism probably proceeded by the pathway for naphthalene metabolism, for they were not metabolized by cured derivatives of strains in which naphthalene metabolism is normally determined by a plasmid, the metabolism of 2-chloronaphthalene was accompanied by the accumulation of a chloro-2-hydroxy-6-oxohexadienoate, and 4- and 5-chlorosalicylate were converted to this compound and themselves induced enzymes for naphthalene and chloronaphthalene metabolism. In one strain, ATCC 17483, it was possible to show that during growth on succinate in the presence of chloronaphthalenes the enzymes of naphthalene metabolism were induced. Failure of 2-chloronaphthalene to support growth was probably associated with the very slow metabolism of the chloro-2-hydroxy-6-oxohexadienoic acid or possibly with the toxicity of this compound or its metabolites.